4.2 Material Grading for Road Construction

  

Road is constructed with wide varieties of construction materials. A large quantity of local as well as non-local materials are consumed during road construction. Local materials contain stone, sand, soil, gravel, chips wood etc. and non-local material contains cement, reinforcement bars, bitumen etc. These local as well as non-local materials are used for the construction of various types of structures such as, retaining structures, pavement works etc. For example, for the construction of road pavement, subgrade soil, sub base course gravel, crushed gravels, dust, bitumen, chips etc. no any construction materials for pavement could be of single size. Grading of particles shall be conducted at laboratory with the application of equipment. Grading of materials are conducted due to following reasons:

• To identify the various characteristics of materials such as degree of compaction.
• To identify the various engineering properties of soil.
• To determine the strength of soil and materials etc.
• To identify the drainage quality of soil and materials used in pavement construction.

Grading of fine as well as coarse aggregates are required according to the type of pavement and its construction process. Grading of construction materials for concreting, masonry mortar may differ from the materials for pavement construction. Generally, gradation of aggregates used in road construction can be performed with sieve analysis. Sieve analysis helps to determine the particle size distribution of the coarse and fine aggregates. Following procedure are to be followed to determine particle size distribution of Aggregates:

• The test sample is dried to a constant weight at a temperature of 110 + 5 °C and weighed.
• The sample is sieved by using a set of IS Sieves.
• On completion of sieving, the material on each sieve is weighed.
• Cumulative weight passing through each sieve is calculated as a percentage of the total sample weight.

By grading of aggregates following information can be obtained:

• Fulfillment of gradation requirement of road construction aggregates.
• Percentage of flaky of single sized particles present in the materials volume.
• Percentage of every stages of gradation requirement as per road specification.
• A Flakiness index, aggregates impact value, aggregate crushing value and other desirable values can be determined after gradation of materials.